Inhibition of polymerization



Unite States This application is a division of my earlier application Serial No. 287,516 filed June 13, 1963.

This invention relates to a method for inhibiting the polymerization of polymerizable unsaturated organic monomers.

It is well known that polymerizable unsaturated organic monomers are denatured when they are transferred or stored at room temperatures or subjected to elevated temperatures, such as encountered during distillation of monomers.

It is also well known that stabilizers are added to the monomers in order to avoid such denaturation. However, it has also been experienced that polymers are colored when the polymer is made from the monomers containing stabilizers, t-butylcateohol, hydroquinone and p-methoxyphenol, for example, which are familiar stabilizers for acrylonitrile, acrylates or methacrylates reduce whiteness or the thermal stability in whiteness of polymers thereof, and sometimes they inhibit polymerization to adversely aiiect the polymerization yield and molecular weight distribution, even if they are contained in the monomers in a minor amount. Accordingly, the monomers should be thoroughly purified before they are polymerized, with the result that they require severe distillation and consequent loss of monomer.

It is an object of the present invention to provide new stabilizing agents for polymerizable unsaturated organic monomers which avoid denaturation of the monomers and do not color polymers obtained therefrom.

It is another object of the present invention to provide new stabilizing agents for polymerizable unsaturated organic monomers which give polymers superior thermal stability in whiteness, even if the stabilizers remain there- It is a further object of the present invention to provide a method for stabilizing polymerizable unsaturated or ganic monomeric compounds.

According to the present invention, compounds represented by the general formula of wherein X represents a sulphur or oxygen atom are admixed with polymerizable unsaturated, organic compounds.

The polymerizable, unsaturated organic compounds according to this invention are styrene and alkyl substituted compounds thereof e.g. p-methylstyre'ne, etc. The following compounds are also stabilized by the substances according to the invention but are the subject of my parent application and divisional applications Serial Nos. 482,657 and 482,659: acrylonitrile and alkyl substituted compounds thereof, e.g., methacrylonitrile, dimethyl acrylonitrile, etc.; acrylic acid and its alkyl substituted compounds thereof, e.g., methacrylic acid, ethacrylic acid, etc.; and alkyl esters of such acids, e.g., methyl methacrylate, ethylmethacrylate, butylmethacrylate, methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc.; and amides of such acids, e.g., acrylarnide, methacrylamide, etc.; vinyl esters, e.g., vinyl acetate, vinyl propionate, etc.; vinyl and vinylidene halides, e.g., vinyl chloride, vinylidene chloride, etc.; vinyl compound containing sulfonic acid groups, e.g., vinyl sulfonic acid, methallyl sulfonic atet acid, p-styrene sulfonic acid, etc.; vinyl compounds containing basic nitrogen atom, e.g., Z-methyl-S-viny-l pyridine, 4- vinyl pyridine and N,N-diethylaminoethyl-methacrylate.

The compounds to be added include acetonethiosemicarbazone, acetaldehydethiosemicarbazone, acetophenonethiosemicarbazone, acetylthiosemicarbazide, phenylthiosemicarbazide, formylthiosemicarbazide, carbaminylthiosemicarbazide, thiosemicarbazide, acetonesemicarbazone, acetaldehydesemicarbazone, acetophenonesemicarbazone, acetylsemicarbazide, semicarbazide, phenylsemicarbazide and iononesemicarbazone.

The stabilizer comounds may be used in an amount of 0.5 to 2000 p.p.m., preferably 1-50 p.p.m.

These stabilizers produce no adverse effects when monomers having the stabilizers are subjected to polymerization in the presence of peroxide or redox type catalysts.

Example 1 In order to show the effectiveness of the present inhibitors in comparison with other known inhibitors a test was carried out in which acrylonitrile containing the inhibitors to be compared was subjected to the oxygen bomb test, which is conventionally employed for determining the stability of gasoline in the presence of oxygen at high pressures. This test was carried out as follows:

Using a graduated cylinder, 25 ml. of acrylonitrile containing the inhibitor was introduced into the glass liner. The liner was placed in the stainless steel bomb, connected to a pressure recording gauge and the bomb was closed tightly. Oxygen was added to a pressure of pounds per square inch gauge at room temperature. The bomb was placed in a steam bath and the pressure characteristics were noted over a four-hour period.

As the bomb becomes heated, the pressure rises gradually to about pounds per square inch gauge. If the sample is potentially unstable, the pressure, after levelling off, will drop, then increase rapidly, and the acrylonitrile will become a solid polymer. If no sudden pressure drop is noted, and if no solid polymer is formed during the four-hour test period, the inhibitor is considered satisfactory.

The above test was applied to acrylonitrile containing the following inhibitors. Tertiary butyl catechol, hydroquinone monomethyl ether, thiosemicarbazide, acetaldehydet-hiosemicarbazone, acetonethiosemicarb-azone, acetophenonethiosemicarbazone, semicarbazide, acetonesemicarbazone, acetaldehydesemicarbazone. The table mentioned hereinunder shows the concentrations as well as the effect upon the acrylonitrile.

COMPARISON OF INHIBITORS Tertiary butyl catechol 100 p.p.m., sample polymerized.

Hydroquinone monomethyl ether 10 p.p.m., sample polymerized.

Hydroquinone monomethyl ether 20 p.p.m., no polymer formed.

mer formed.

The above data show that the inhibitors according to the present invention are effective at lower concentrations than the conventional inhibitors of the prior art. In addition to this superiority in that a smaller amount of the inhibitors is necessary, the present inhibitors have the further advantages of negligible color formation. In addition to the above accelerated stability test carried out in the presence of oxygen at elevated temperatures and high pressures, it has been found that the present inhibitors are effective in prolonged storage under normal atmospheric conditions.

Acrylic fibre was prepared by polymerizing acrylonitrile (containing the inhibitor), without removing the inhibitor, dissolving in 55-80% nitric acid. The thermal stability in whiteness of the acrylic fibres thus prepared were very good and showed negligible color formation.

Example 2 In order to show the effectiveness of the present inhibitors in comparison with other known inhibitors a test was carried out in which acrylic esters, such as methylacrylate, ethyl acrylate and butyl acrylate, and methacrylic esters such as methylmethacrylate containing the inhibitors to be compared was subjected to a viscosity test which was carried out as follows:

In a 100 cc. Erlenmeyer flask, an inhibitor and 0.025 gram of 2,2'-azobisisobutylonitrile is dissolved in 60 grams of acrylic ester or methacrylic ester. This flask is placed in a thermostat maintained at 60 C.,'The viscosity of 5 cc. samples taken at fixed intervals from the flask is measured by an Ostwald viscosimeter. When the viscosity fails to rise abruptly within 6 hours, the inhibitor is considered effective.

The above test was applied to methyl acrylate, ethyl The above data show that the present inhibitors are effective at lower concentrations than the conventional inhibitors of the prior art. In addition to this superiority in that a smaller amount of the inhibitors is necessary, the present inhibitors have the further advantages of negligible color formation. In addition to the above accelerated stability test carried out, it has been found that the present inhibitors are effective in prolonged storage under normal atmospheric conditions.

Example 3 Effectiveness of the present inhibitors was investigated. Monomers to which the inhibitors were added Weighed 100 g., respectively and were left to stand under atmospheric pressure, at room temperature for one year, except for vinylchloride in a bomb for one year, to observe changes of viscosity as well as appearance.

TAB LE Monomers Inhibitors Cone. Viscosity Appearance Acrylonitrile Thiosemearbazide 30 Unchanged. Unchanged. Methaerylonitrile Acetonethiosemicarbazone 30 do Do. Acrylic acid Acetylthioserniearbazide Do. Methaerylie acid. Semicarbazide Do. Ethacrylie acid Acetonesemicarbazone. Do. Methy1methacrylate Acetaldehydesemiearbazone. Do. Ethylmethacrylate... Accta1dehydethiosemicarbazone Do. Butylmethacrylate Phenylsemiearbazide Do. Methylacrylate Acetonethiosemicarbazone Do. Ethylacrylate Thioserniearbazide Do. Prepylacrylate. Acetonosemiearbazone D0. Butylaerylate Acctaldehydeserniearbazone. Do. Styrene Acetonethiosemiearbazone- Do. p-Methylstyrene Semiearbazide Do. Vinylacetatm. Acetaldehydethiosemiearbazi e Do. Vinylchloride Acetaldehydesemicarbazone.. Do. Vinylideneehlori e Semicarbazide D0. Vinylsulfonic acid Phenylsernicarbazide--. Do. Methallylsnlfonic acid. Acetonethiosemiearbazone Do. p-Styrene sulfonic acid.. Thiosemicarbazide Do. Z-methyl-fi-vinyl pyridine .do Do. 4-vinylpyridine Aeeta1dehydethiosemicarbazone.. D0. N ,N-dlimethylamiuoethylmeth- Semiearbazide D0.

acry ate.

acrylate, butyl acrylate and methylmethacrylate containing the following inhibitors:

Hydroquinone monomethyl ether methacrylic esters.

It will be seen from the above table that lower amount of the present inhibitors than conventional ones is sufficient to stabilize the various polymerizable organic mono- 65 mers. Furthermore, the present inhibitors do not color Thlosemlc-arbazl-de the monomers at all. Acetonethiosemicarbazone What I claim is. Aceiylthlosimlcarbazlde 1. A method comprising stabilizing a polymerizable semlcarbazlfie monomer selected from the group consisting of styrene 70 and p-methylstyrene by adding to said compound 0.5 phenylsemlc'arbgzlde. to 2,000 ppm. respectively of at least one stabilizer Acetaldehydethlosemlcapbazone selected from the group consisting of acetonethiosemi- The table hereinunder mentioned shows the concencarbazone, acetophenonethiosemicarbazone, acetoaldetrations as well as the effect upon the acrylic esters and hydethiosemicarbazone, acetylthiosemicarbazide, phenylthiosemicarbazide, formylthiosemicarbazide, carbaminylthiosemicarbazide, thiosemicarbazide, iononethiosemicarbazone, acetonesemicarbazone, acetoaldehydesemicarbazone, acetophenonesemicarbazone, acetylsemicarbazide, phenylsemicarbazide, iononesemicarbazone, and semicarbazide, and polymerizing said monomer in the presence of said stabilizer to produce'a polymer which is thermally stable and is free from coloration by said stabilizer.

2. A composition comprising a polymer which is a product of a polymerizable monomer selected from the group consisting of styrene and p-methylstyrene, and 0.5 to 2,000 ppm. respectively of at least one stabilizer selected from the group consisting of acetonethiosemicarbazone, acetophenonethiosemicarbazone, acetoaldehydethiosemicarbazone, acetylthiosemicarbazide, phenylthiosemicarbazide, forrnylthiosemicarbazide, carbaminylthiosemicarb-azide, iononethiosemicarbazone, acetonesemicarbazone, acetoaldehydesemicarbazone, acetophenonesemicarbazone, acetylsemicarbazide, phenylsemicarbazide, iononesemicarbazone, and semicarbazide.

3. A method comprising stabilizing a polymerizable monomer selected from the group consisting of styrene and p-methylstyrene by adding to said compound 0.5 to 2,000 ppm. respectively of at least one stabilizer selected from the group consisting of acetonethiosemicarbazone, acetophenonethiosemicarbazone, acetoalde-hydethiosemicarbazone, acetylthiosemicarbazide, phenylthiosemicarbazide, formylthiosemicarbazide, carbaminylthiosemicarbazide, t-hiosernicarbazide, iononethiosemicarbazone, acetonesemicarbazone, acetoaldehydesemicarbazone, acetophenonesemicarbazone, acetylsemicarbazide, phenylsemic-arbazide, iononesemicarbazone, and semicarbazide,

said styrene compound being adapted for undergoing polymerization in the presence of said stabilizer to produce a polymer which is thermally stable and is free from coloration by said stabilizer.

4. A composition comprising a polymerizable monomer selected from the group consisting of styrene and p-methylstyrene, and 0.5 to 2,000 ppm. respectively of at least one stabilizer selected from the group consist-- References Cited by the Examiner UNITED STATES PATENTS 2,299,128 10/ 1942 Codd et al. 252-403 X 2,328,190 8/1943 Burk et al 26240 2 X 2,353,690 7/1944 Clarkson et a1. 2-40 2 X 2,396,156 3/ 1946 Clarkson 252 2 X DELBERT E. GANTZ, Primary Examiner.

S. P. JONES, Assistant Examiner. 

2. A COMPOSITION COMPRISING A POLYMER WHICH IS A PRODUCT OF A POLYMERIZABLE MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE AND P-METHYSTYRENE, AND 0.5 TO 2000 P.P.M. RESPECTIVELY OF AT LEAST ONE STABILIZER SELECTED FROM THE GROUP CONSISTING OF ACETONETHIOSEMICARBAZONE, ACETOPHENONETHIOESEMICATBAZONE, ACETOALDEHYDETHIOSEMICARBAZONE, ACETYLTHIOSEMICARBAZIDE, PHENYLTHIOSEMICARBAZIDE, FORMYLTHIOSEMICARBAZIDE, CARBAMINYLTHIOSEMICARBAZIDE, IONOETHIOSEMICARBAZONE, ACETONESEMICARBAZONE, ACETOALDEHYDESEMICARBAZONE, ACETOPHENONESEMICARBAZONE, ACETYLSEMICARBAZIDE, PHENYLSEMICARBAZIDE, INONESEMICAARBAZONE, AND SEMICARBAZIDE. 